Corvo stood up straight, staring down at the puddle of blood that was creeping toward his right foot. The back of his left hand still stung and burned in the familiar way it did whenever he used the Outsider's powers. He twirled his blade and folded it up, holstering it on his side before using his right hand to scratch at the back of his left. He blinked a few times, looking down at the body in front of him.
The first few times Corvo had killed after the Outsider appeared to him in that horrible nightmare, it had been difficult to accept. It was hard to believe that he'd received these powers, let alone to see his own hands reach out and use them to cause the demise of other people. People in his way, to be sure, and evil people, certainly. However, they were still people.
As the Outsider's chosen looked down through the lens of his mask, he pondered on the twist of fate that had caused his victim to die. It certainly hadn't been his intention - though he should have been more careful.
One of Daud's assassins had been walking down the street, and Corvo had jumped off of the ventilation shaft he'd been perched on. As he fell through the air, his blade twirled out and unfolded, only sinking into the assassin's flesh just before Corvo would have hit the ground himself.
He hadn't been sure about leaving the body in the middle of the street, and when the dark power called to him, whispered to him, Corvo answered by raising the half-clawed fingers of his left hand in a shaky motion. Out of the inky blackness, a horde of ravenous rats had come. They'd come and eaten the assassin's body, removing it from the city as if the carcass had never existed. Easy disposal if there ever was any.
So Corvo had begun walking away. Out of the corner of his eye, however, he saw Griff - the old merchant he'd rescued from the Bottle Street Gang - walking down the street at a leisurely pace. He worried for a mere moment, but reasoned that Griff would be smart enough to avoid the rats. And seeing as they'd just fed, they weren't likely to attack him. It was in that moment that Corvo realized he could only summon the rats - he could not directly control them nor banish them.
That was when he heard the screams.
He shut his eyes and mentally called himself a fool. He didn't want to look back - and he didn't. At least, not until the screams of anguish and horror were silenced by the hungry creatures. That's how he'd ended up above the man's bloody and mutilated corpse.
Corvo had the thought that he'd bought some crossbow bolts from this man only minutes before this unfortunate incident. He was unsettled to find that this did not make him feel remorseful. Instead, he felt a darkly light feeling inside him. It was akin to an alcohol buzz, but Corvo had drank nothing recently except for the imagery and sounds of the old man being consumed alive.
The blood had reached Corvo's shoe and he pulled the foot back, streaking crimson across the ground. Morbidly and with a smile of indifference, he wondered how much more humanity he would lose. He also questioned the logic of the vermin he'd brought into the world. Why had they taken specifically the limbs that they had off of Griff?
As he walked away from the corpse and heard the whispers of the Heart in his mind, he was struck by the remembrance that salesmen were often said to take an arm and a leg for the wares they peddled. The irony was not lost on the killer. He smiled a smile with little joy behind it - only madness.